{  Statement: http://acmp.ru/?main=task&id_task=312
   Verdict: Accepted
}
uses
    SysUtils, Math;

var
    a,b,c:int64;
    
begin
reset(input, 'input.txt');
rewrite(output, 'output.txt');
read(a, b, c);
write(a + (b - a) * (c - 1));
end.